1. Field of the Invention
The present invention relates to means, methods and apparatus for sensing the position of the needle within the nozzle of a fuel injector for an internal combustion engine.
2. Background Information
It is possible to improve the efficiency of control of a fuel injection system by sensing whether the injecting nozzle is closed or open. This information can, for example, be used by the electronic control system of the engine to perform adaptive fueling or injection timing control.
Examples of apparatus for sensing the needle position within the nozzle of a fuel injector are generally known, as shown in U.S. Pat. Nos. 4,625,918 and 4,398,670. In these apparatus, the needle is electrically insulated from the nozzle body and the rest of the injector during the open positions of the nozzle by means of an insulating layer placed on the needle""s guiding surface, and it is electrically connected to the nozzle body and therefore to the ground during the closed state of the nozzle. A disadvantage of such apparatus is that they require an electric conductor to be passed through the upper body of the injector for connection of the needle to an external continuity-sensing device. In case of the upper body of the injector being of a complicated design or when the spring chamber of the needle is used to provide a pressure backed nozzle closure, it becomes difficult and non-feasible to accommodate the electrically insulated and hydraulically sealed conductor in the injector""s upper body.
An injection timing sensor disclosed by Milton et al. in the xe2x80x9cDevelopment of a Tuneable Diesel Engine Injection System for Engine Calibration and Optimizationxe2x80x9d, ARC Collaborative Research Project, Final Report, School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia, July 1998 provides a possible solution to this problem by means of insulating the upper body of the injector and including a needle spring chamber, from the ground and the lower body of the injector, and having a nozzle body, in addition to using the insulated needle as described above. In this design, the whole upper body acts as the conductor for connection of the needle to the continuity-sensing device, and therefore the need to pass a sealed and insulated electrical conductor through the upper body of the injector is eliminated.
To insulate the upper and the lower bodies of the injector from each other, an insulating layer similar to the one used for coating the needle may be used. It has to be applied to the thread of the cap nut holding the upper and lower bodies together, as well as to one of the surfaces forming a flat mechanical seal between the bodies. Usually, locating pins are used in the injectors to ensure a fixed angular position of one body of the injector relative to the other during assembly of the injector. Such pins protrude from one body and fit into the matching holes formed in the other body. Therefore, to achieve electrical insulation between the bodies, either the locating pins or the internal surface of the matching holes must be coated with the insulating layer.
In most cases, the diameters of the locating pins and the matching holes are not made exactly the same in order to facilitate easy assembly and reduce manufacturing costs. The relative position of the pins and the holes is also imperfect due to production tolerances. This means that when the locating pins prevent the relative rotation of the upper and lower bodies of the injector during the tightening of the cap nut, a line contact is formed between the pins and the matching holes. Moreover, as the internal surface of the holes is usually formed by drilling, it is difficult to achieve a very smooth surface, so that the contact surface between the pins and the holes might be reduced from the line to a point contact.
It is known that the forces acting on the locating pins due to the friction between the contact faces of the cap nut and the body opposite to the one that is engaged in threaded connection with the cap nut, may be so high that in some cases the pins are sheared apart. If a line or a point contact exists between the pin and the hole and there is an insulating layer on the pin, it is possible that the layer will be destroyed in that point of contact and the insulating barrier between the two injector bodies will be lost, resulting in the failure of the needle position sensor.
The purpose of the present invention is to overcome this problem and therefore increase the reliability of operation of the needle position sensing device.
In accordance with a first aspect of the present invention, there is provided a fuel injector incorporating a position register device, the fuel injector including a first body and a second body; a cap nut which is in a threaded engagement with the first body and has a shoulder for abutting against the second body to hold the first and second bodies together; locating pins for fixing the angular position of the first and second bodies relative to each other; the first and second bodies are electrically insulated from each other by means of an insulating layer; the insulating layer is deposited in such a way as to prevent the electrical contact between the locating pins and at least one of the bodies; an anti-friction layer between the shoulder and the second body; a reciprocating needle moveable within the first and the second bodies for opening and closing a nozzle; position register device electrically connected to the first body, and the second body and position register device each connected to a source of equal potential or ground, wherein the first and second bodies are not electrically connected when the needle is in an open position and wherein the first and second bodies are electrically connected when the needle is in the closed position.
In a second aspect the present invention is similar to that described above, but the layer, which is used to insulate injector the first and second bodies of the fuel from each other, possesses an anti-friction property and is therefore used between the shoulder and the second body instead of the anti-friction layer, wherein a connector is used to electrically connect the second body to the ground.